1. Field of the Invention
The present invention relates to a printing head of the spring release type.
2. Description of the Prior Art
A typical arrangement of a well-known spring release type printing head includes driving arms for driving printing elements formed on a resilient plate, the driving arms being biased by the magnetic flux of a permanent magnet by means of an electromagnetic driving device provided with the permanent magnet and a demagnetizing coil, the biased driving arms being released by offsetting the magnetic flux of the permanent magnet as the coil is excited, thus driving the printing elements via the driving arms. In a spring release type printing head, prevention of flexures of the driving arms towards a platen immediately after the printing elements have impinged on the platen involves the use of a stopper provided for the resilient plate (e.g., Japanese Patent Laid-Open Publication No. 54-13147), or an auxiliary resilient plate disposed in parallel (e.g., Japanese Utility Model Publication No. 62-24530).
It cannot, however, be said that the prior art structures described above are capable of completely eliminating flexures of the driving arms towards the platen. More specifically, in a spring release type printing head, when the printing element collides with the platen after releasing the armature of the driving arm, the armature further moves toward the platen with inertia, while the driving arm undergoes reaction because of the platen, resulting in an S-shaped flexure. For this reason, the impact-time of the printing element increases, thereby not only hindering speed-up of the printing process but also causing vibrations for a short period of time until the resilient plate subjected to the S-shaped flexure reverts to a normal state. The vibrations in turn hinder peculiar motions of the armature, and it follows that double printing and print skipping take place. Besides, stress on the armature system increases in magnitude, which in turn exerts adverse influences on the durability.
The prior art arrangements described above entail a complicated configuration of a highly rigid material to construct a stopper, and for this reason defects result which require additional time for processing and involving costly production.